A draft U.S. Senate bill aimed at making it easier for organizations to share cyberthreat information poses serious threats to personal privacy, several rights groups said in a letter to Congress on Thursday.

A discussion draft of the Cybersecurity Information Sharing Act of 2014 (CISA) was released last week by Senate Intelligence Committee Chair Dianne Feinstein (D-Calif.). The proposed bill would facilitate a vast flow of information to the National Security Agency at a time when the agency faces many questions about its surveillance practices, the groups said in the letter.

The bill ignores many civil liberties protections incorporated into an earlier version, called the Cybersecurity Act of 2012, the letter said.

The letter, addressed to Feinstein and committee vice chairman Saxby Chambliss (R-Ga.), was signed by the Center for Development of Technology (CDT), the American Civil Liberties Union, the Electronic Frontier Foundation and several other groups.

The CISA bill is designed to let companies more easily share, receive and use information about cyberthreats. It would also provide some protections for companies that engage in countermeasures to deal with attacks against their networks.

Backers of the legislation believe that such measures are needed to help private companies detect and respond to cyberthreats more efficiently. Sharing information about things such as bad IP addresses or malware can help companies more quickly respond to common threats, the supporters say.

The privacy groups, though, contend that CISA would also authorize a free flow of real-time threat information between the private sector and U.S. government agencies, including the NSA and the Department of Homeland Security.

The legislation would require the DHS to immediately disseminate any threat information it receives from private companies to other agencies, such as the Department of Defense and the U.S. Cyber Command, and that could lead to a unnecessary militarization of cybersecurity issues, the letter said.

"This new flow of private communications information to NSA is deeply troubling given the past year's revelations of overbroad NSA surveillance," the groups said in their letter. "It would enhance the NSA's role in the civilian cybersecurity program, risking militarization of the program."

The bill is vague on the specific instances under which companies can share data or what type of information can be shared, the groups said. In addition, there are few clear restrictions on how government agencies can use threat data received from private companies, and inadequate controls for protecting personally identifiable data, they said.

The concerns raised in the letter are similar to those that surfaced during debates over the controversial Cyber Intelligence Sharing and Protection Act (CISPA), a measure that sought to enable the same kind of information sharing proposed by CISA. The bill passed through the U.S. House in 2012, but has failed to make it through the Senate.

John Pescatore, director of emerging security threats at the SANS Institute, said the CISA bill would be unlikely to spur any significant increase in information sharing.

"It does try to address liability and antitrust concerns, and demand that the government protect and not retain such data. But the reality is that there is still little to gain by private industry voluntarily forwarding more information to the federal government. There are existing forums, like the [Information Sharing and Analysis Centers], where such sharing already takes place at the level which makes sense for businesses," Pescatore said.

Enabling better information sharing is a good idea in principle, according to Chris Pierson, chief security officer at Viewpost. "Without bi-directional sharing, companies will face rising threats without any ability to know where they are coming from or [how to] mitigate them," he said.

"At the end of the day, companies will compete on products and services, but sharing known bad IP addresses or command-and-control servers is unlikely to upset competitiveness or [intellectual property]," Pierson said. "The 'how' has to be figured out, but certainly making it easier to share nonsensitive, non-personally identifiable information, and non-trade-secret information could afford all companies greater security."